How to beat Shadow Demon in lane?

In a side lane the rules change a bit since most support Shadow Demon's seem to not grab Shadow Poison in favour of more Soul Catcher  and Disruption for easier kill potential for their carry. If he is paired with a Slardar, you are in a butt load of trouble if he can disrupt you before you can go on him. I personally have trouble against those that are aggressive before I can initiate or those with a good escape, also, landing Soul Catcher is a real bitch if you are near creeps, so keep that in mind.If Shadow Demon gets more then 3-4 stacks of his poison on you, back off. If he gets a disruption at that point, it likely means Soul Catcher, 2 illusions and more stacks of Shadow Poison to deal with, which usually ends up with a death. Magic Wand is your friend, and if you are ranged then try to poke him down since there isn't too much he can do. If you are melee like Pudge or Magnus however, you may have a lot of issues since it will be much easier for him to land poison stacks.

Shadow Poison is pretty easy to dodge

• If you see him spamming it, then he might not have his other two spells which are stupid good. I'd just try to kill him with your teammate. He's pretty easy to kill if he doesn't know how his other spells work.
• He'll probably run out of mana spamming poison or not have enough for his other spells which are used for crowd control and killing
• Magic Stick is good against anyone retarded enough to spam spells
• Try to avoid taking stacks of Shadow Poison. Minimize your time going for creep kills.

It's also useful to know how Shadow Demon works:

Shadow Poison

• For stacks 1-4, it is exponential (i.e. 1x, 2x, 4x, 8x)
• For stacks 5+ it just adds 50 magic damage (i.e. if you already have 4 stacks, a 5th stack isn't going to be that bad)
• When maxed out and at 4+ stacks, this spell can do a shit ton of damage
• It's also amplified by Soul Catcher, which increases damage taken by a %

Disruption

• This spell can be used offensively or defensively
• Offensively - used to set up kills by keeping you in a spot. Another hero can come along and set up a stun on you; Late game, the illusions can be used aggressively if you Disrupt a fed carry or something.
• Defensively - used to protect allies (or self) once initiated upon
• It creates 2 illusions that disappear pretty quickly (like 8 sec at max level)
• This spell is why Shadow Demon is sometimes considered a "counter" to Anti-Mage. The Illusions he makes of Anti-Mage get  Mana Break. While in lane, the Illusions burn a ton of Anti-Mage's mana to the point he might not be able to blink away.

Soul Catcher

• This spell selects a random target in its AoE to affect (i.e. you want them Disrupted so you can guarantee they're the only target in the AoE)
• Amplifies damage on the target by 50% at max level

Demonic Purge

• Removes buffs, slows you, does damage
• The slow goes through Black King Bar (i.e. decent against heroes like Lifestealer )